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Ch.18 - Aqueous Ionic Equilibrium
Tro - Chemistry: A Molecular Approach 6th Edition
Tro6th EditionChemistry: A Molecular ApproachISBN: 9780137832217Not the one you use?Change textbook
All textbooksTro 6th EditionCh.18 - Aqueous Ionic EquilibriumProblem 56c
Chapter 18, Problem 56c

Determine whether or not the mixing of each pair of solutions results in a buffer. c. 225.0 mL of 0.10 M NH3 ; 250.0 mL of 0.15 M NH4Cl

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Identify the components of the solutions: NH3 is a weak base and NH4Cl is its conjugate acid.
Calculate the moles of NH3 using the formula: moles = concentration (M) x volume (L).
Calculate the moles of NH4Cl using the formula: moles = concentration (M) x volume (L).
Determine if the solution can act as a buffer by checking if both the weak base (NH3) and its conjugate acid (NH4+) are present in significant amounts.
Conclude that the mixture forms a buffer if both components are present in comparable amounts, allowing the solution to resist changes in pH.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Buffer Solutions

A buffer solution is a system that resists changes in pH upon the addition of small amounts of acid or base. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, the combination of ammonia (NH3) and ammonium chloride (NH4Cl) can create a buffer because NH3 is a weak base and NH4Cl provides the conjugate acid (NH4+).
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Buffer Solutions

Weak Bases and Conjugate Acids

Weak bases are substances that partially dissociate in solution to produce hydroxide ions (OH-). Ammonia (NH3) is a common weak base. When it is mixed with a salt like ammonium chloride (NH4Cl), which dissociates to provide NH4+, the resulting solution can maintain a relatively stable pH, characteristic of buffer solutions.
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Conjugate Acid-Base Relationships

Henderson-Hasselbalch Equation

The Henderson-Hasselbalch equation is a mathematical formula used to calculate the pH of a buffer solution. It relates the pH to the pKa of the weak acid and the ratio of the concentrations of the conjugate base and the weak acid. For the NH3/NH4Cl system, this equation can help determine the effectiveness of the buffer in maintaining pH when acids or bases are added.
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Related Practice
Textbook Question

Determine whether or not the mixing of each pair of solutions results in a buffer. b.155.0 mL of 0.15 M NH3 ; 155.0 mL of 0.10 M HCl

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Textbook Question

Blood is buffered by carbonic acid and the bicarbonate ion. Normal blood plasma is 0.024 M in HCO3- and 0.0012 M H2CO3 (pKa1 for H2CO3 at body temperature is 6.1).

c. Given the volume from part (b), what mass of NaOH can be neutralized before the pH rises above 7.8?

Textbook Question

Determine whether or not the mixing of each pair of solutions results in a buffer. d. 150.0 mL of 0.15 M HCl; 135.0 mL of 0.25 M NaOH

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Textbook Question

Determine whether or not the mixing of each pair of solutions results in a buffer. a. 155.0 mL of 0.15 M NH3 ; 175.0 mL of 0.17 M HCl

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Textbook Question

Blood is buffered by carbonic acid and the bicarbonate ion. Normal blood plasma is 0.024 M in HCO3- and 0.0012 M H2CO3 (pKa1 for H2CO3 at body temperature is 6.1).

a. What is the pH of blood plasma?

Textbook Question

Determine whether or not the mixing of each pair of solutions results in a buffer. c. 55.0 mL of 0.15 M HF; 85.0 mL of 0.10 M NaF

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